The present invention relates to a golf club head composed of a metallic main body and a FRP part, more particularly to a layered structure of the FRP part.
In recent years, hollow metal wood-type golf club heads are widely used. In order to reduce the weight of such hollow head and to lower the center of gravity, a hybrid head whose main body is made of a metal material and provided in the crown portion with an opening covered with a light-weight FRP part have been proposed. According to common belief to decrease the energy loss at impact, a resinous material whose internal friction on deformation is small is usually used to make such a FRP cover.
In the recent wood-type golf club heads, on the other hand, there is a trend toward large head volume. Thus, the opening in the crown portion and the FRP cover also have a tendency to become large sized.
The face portion receives a large impulsive force when hitting a ball. As a result, the face portion leans back instantaneously, and the FRP cover is deformed and starts to vibrate. As the internal friction is small, the duration of vibrations becomes relatively long although it is absolutely short. The impulsive force superposed by such vibrations is felt as a large shock, sometimes being painful by the golfer's hands. Further, such a resinous material has a tendency to have a poor impact-resistance. Therefore, there is a high possibility that the FRP cover is broken or cracked in transport or in play.